The present invention relates generally to an apparatus for cutting spirally formed pipe, and more particularly, to an apparatus for cutting relatively short lengths of pipe having a diameter of one inch or less.
Several machines use inner and outer knives to cut a continuously formed spiral pipe. Such pipe cutting machines are disclosed in my U.S. Pat. No. 4,706,481, 4,823,579 and 4,924,684, issued Nov. 17, 1987, Apr. 25, 1989 and May 15, 1990. In those machines, an inner knife is attached to a boom, and an outer knife is positioned outside the pipe. To cut the pipe, the outer knife is moved into an overlapping relationship with the inner knife. As the pipe rotates and moves axially, the overlapping knives move axially with the pipe and cooperate to cut the pipe. Since the pipe must complete one revolution to be severed, the axial distance the pipe moves during the cutting operation limits the length of pipe which can be cut. By the time the knives return to a begin-cut position, the pipe has already moved too far to cut a relatively short section of pipe. In addition, the pipe undergoes stress during the cutting operation, thus making it more difficult to form the pipe within a forming head and move it axially. On the contrary, the present invention includes an inner knife which is moved radially outward and actively revolved around the interior periphery of the pipe in the same direction the pipe is rotating. As a result, shorter lengths of pipe can be cut because the pipe is severed before it has completed one revolution, and the stress on the pipe is reduced to enhance formation of pipes having a diameter of one inch or less.
U.S. Pat. No. 957,966 (Jenkins) discloses an apparatus which cuts a spirally wound paper tube before it has completed one revolution. In the Jenkins apparatus, an inner support disk is used rather than an inner knife, and the pipe is engaged by moving a plurality of outer knives inward rather than moving an inner knife outward. Also, the present invention includes an annular outer knife which cooperates with the inner knife around the entire circumference of the pipe. In practice, it would be difficult for the Jenkins apparatus to cleanly cut a metal pipe since only outer knives perform the cut and the outer knives independently cut the tube in different locations. It would also be difficult to position more than two knives' outside a pipe having a diameter of one inch or less. Furthermore, the formation of smaller diameter pipes would be more difficult since the outer knives are not actively revolved around the pipe in the same direction the pipe is rotating.
The pipe cutting machines in U.S. Pat. No. 3,268,137 (Martin), U.S. Pat. No. 3,913,430 (van Dijk), and E.P. Patent 353,622 (Harrop) disclose knives which are actively revolved around the pipe to perform a cut. In Martin, an outer cutter is positioned inside a cutter housing, and the cutter housing is positioned inside a cam collar. The cam collar is moved axially to force the cutter housing and outer cutter inward until the cutter engages a pipe manually placed therein. The entire assembly is then rotated to cut the pipe. This machine is not used for cutting continuously formed spiral pipe, and no inner knife is provided.
Van Dijk discloses a device for cutting rings from a pipe. The pipe is manually placed inside a die, inner cutters are moved radially outward by levers to engage an interior surface of the pipe, and the cutters are revolved around the circumference of the pipe. This machine also is not used for cutting continuously formed spiral pipe, and no outer knife is provided. Moreover, it would be difficult to fit two knives and all the connected components shown in Van Dijk inside a pipe having a diameter of one inch or less.
In Harrop, a rotary unit is positioned inside a cam ring, and a pair of outer knives are slidably mounted in the rotary unit. When a desired length of pipe has been reached, the feed of strip and formation of pipe is halted. The rotary unit is moved axially and the outer knives are forced radially inward to engage the pipe. The rotary unit is then rotated and the outer knives cooperate with a mandrel to cut the pipe.
None of these machines cut a continuously formed spiral pipe by using an annular outer knife in cooperation with an inner knife which is moved radially outward and actively revolved around the interior periphery of the pipe. Furthermore, it would be difficult to use the machines mentioned to cut a spiral pipe having a diameter of one inch or less.